Repeater circuits for multiplex systems



June 21 1927. 1,632,909

J. 5. JAMMER REPEATER CIRCUITS FOR MULTIPLEX SYSTEMS Filed July 6. 1921 m vervanc/aco 5. dam/776v"; I

Patented June 21, 1927.

UNITED STATES PATENT oFFIcE.

JACOB S. JAHMER, CUMBERLAND, MARYLAND, ASSIG NOR '1O WE STEBN ELECTRIC COMPANY, CORPORATED, OF NEW YORK, N. Y., A CORPORATION 01' NEW YORK.

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Appllcltion filed July 8,

'This invention relates to a repeater circuits, and more particularly to amplifying repeater circuits of the type-which comprises a air of vacuum discharge devices 5 ofthe grid type having their grid circuits oppositely connected to aninput line or circuit. Such repeaters areused in signaling systems for amplifyin signaling waves at various points along t e transmission line and .are' especially applicable in multiplex telephone and telegraph systems.

' In multiplex systems it is extremely desirable to prevent the repeater from modulating a wave of one frequency by a'wave of another frequency. Repeater circuits of thetype described tend to cause srch modu-' 'lation. This causes cross-talk and interference between the various channels. In order to prevent modulating action in such 2 a repeater it has been proposed heretofore to use in the plate circuits of each of the vacuum tubes constitutin one stage of the repeater a choke coil of highinductance. Such choke coils are located in shunt to the 5 alternating current output circuit. It has been found that their use results in much more nearly distortionless repeating and hence less intermodulation of waves of dif ferent frequencies. On account of the large number of turns necessarily included in the windingsof such coils in order to produce the required inductance an iron core of con-- siderable size must be-provided to carrythe flux resulting from the direct current through the coil; otherwise with a small core, the core would be magnetically saturated with a consequent loss of inductive effect. The cost of coils for such purposesmay be decreased by decreasing the size of the core. To gain this'and other advantages it is proposed herein to use a single coil in place of the two coils heretofore used.

By passing the direct s ace current of one tube through one half 0 the turns in such a direction as.to tend to set up a fluxin o position to that set u by the current in t e other half the norms flux in the coil is re-' duced to zero. The core may therefore be only sufliciently large to carry the maximum uxresulting from the currents produced by signaling electromotive forces impressed upon the coil. Thus, there is accomplished with a single small core what has been previously accomplished in such distortionlem 'Jrepeaterswith two large core coils. Fur- 1921.. Serial ir -182,708.

thermore, and what is-of some importance, ezerperimental tests have indicated a further r notion in distortion with this arrangement as ,compared with that wherein two foils are used, other conditions being simiar. ofkeeping the direct space current paths separate from the alternating space current paths are retained. Furthermore the ad-'- vantage of using the space current source of the repeater as a common space current supply to other repeaters in the same station 1 is also retained. Except for the resistance drop in. the choke coil itself the total electromotive force of the space current source is impressed on the tubes. An important essential of distortionless repeaters of the kind described is that the two sides of the circuit must be balanced with .respect to each other, with respect to round, and with respect to the incoming and outgoing lines. The difliculty ofmaintaining this balance is not increased by the means described. herein. The invention is described below in detail in connection with the accompanying-drawing, which is a circuit dia am of a twostage repeater having the c aracteristically novel features of the invention applied to the output circuit of the first stage.

The repeater circuit is intended to repeat signaling waves from the input line 1 to the output line 2 with amplified energy. The input line 1 iscoupled by means of a trans- It will be noted. that the advantages former 3 having a divided secondary wind-- comprises condensers 8 and impedance ele-,-

ments 9. Under some cirrcumstances the impedance elements 9 may be resistance elements, but if desired the switches 10 may be moved to place in circuit the inductive impedance elements 11 in place of the elements 9. When inductance elements 11 are in circuit the variable taps on the elements 9 may be moved to cut out of circuit all or a part of the elements 9 as may be desired.- The anodes 7 are connected together through the inductive choke coil 12 which has twoparts 13 and 14. The parts 13 and 14 typify any equivalent arrangement of coils having a highratio of mutual inductance as compared with A n ected together through connection 15 extends from the electrical midpoint of the coil 12 to the positive side of a space current battery 16. Space current is supplied to the tubes 6 through the connection 15 and the two halves of the winding of the coil 12 is parallel, each half constituting the path to one tube. The nor mal flux in the core of the coil 12 will be zero, provided equal currents traverse the two halves of the coil, since these currents pass around the coil in opposite directions. A. condenser 17 is shunted around the but tciy 16. The battery 16 may be used for otherrepeaters in the same station as indicated by the circuit 18 which may extend to as many repeaters as the battery 16 can supply, the return path for each being through ground. l

A second stage of the repeater is provided for reamplifying the output of the first stage before impressing it upon the output line 2. This second stage consists of the vacuum tubes 19 whose grid circuits are connected to the energy transferring impcdanccs 9 or 11, and whose anode circuits 20 are coupled to the output line 2 through the transformer 21.

Since any modulated waves produced in the first stage of the repeater are amplified by the second stage they are much more troublesome than would be modulated waves produced in the second stage; hence the invention as exemplified by the coil 12' has not been applied to the anode circuits of the tubes 19. Furthermore if a high mutual inductance exists between the halves of the primary of the transformer 21, this will tend to reduce modulation in the second stage. Nevertheless the invention could be applied to the second stage of therepeater system in the same manner in which it is applied to the first stage, if desired. Such application is believed to be obvious, and it is therefore not described. It should be said, however, that modulated waves produced in the first or foremost stages of a plural stage repeater cannot be eliminated by applying the invention to the last or succeedin stages, since, in general, except as equalizing or discriminating net works are used between stages the components present in the output of any particular stage are equally amplified in a succeeding stage or stages. For this reason it is more essential, as stated above, to eliminate-modulation and distortion in the first stage of a repeater, than it is to eliminate it in the succeeding stages.

Having described one'form of the invention in detail. the novel features believed to be inherent therein will be set forth in the appended claim.

\Vhat is claimed is:

An amplifier circuit for preventing modulation during repeating and comprising a pair of space discharge devices, each-having a cathode, an anode and a grid element,

an incoming circuit, an outgoing circuit,

means connecting said incoming circuit differentially to the grid and cathode elements of said two devices, means connecting the cathode and anode elements of said devices equally and oppositely to said outgoing circuit, said last mentioned means including a coupling impedance with its mid-point connected to the cathodes of said devices and having its outer terminals connected through respective wave transmission paths to the anodes of said devices, and means supplying space current between the cathodes and anodes of said devices comprising a source of current and a pair of windings on a unitary core, said windings having a common terminal connected through said source of current to said cathodes and the outer terminals connected to said anodes, the direction of said windings being such that the windings oifer low impedance to current components of the same sign flowing simultaneously between their common terminal and the outer terminals but offering high impedance to components tending to flow from one anode terminal to the other whereby said winding and core structure discriminates against the transmission to the outgoing circuit of the undesired components with respect to the desired components.

In witness whereof, I hereunto subscribe my name this 30th day of June A. 1)., 1921.

JACOB S. J AMMER. 

